Method for manufacturing an optical gate device containing a large-area grown transition metal dichalcogenide as a photosensitive layer

Abstract

An optical gate element that can respond to optical stimuli and has a photosensitive layer that exhibits neuromorphic properties, and a method for manufacturing the same, are provided. [Solution] A method for manufacturing an optical gate element, which is a logic element that performs AND or OR logical operations, includes the steps of: preparing a first heating furnace and a second heating furnace that are arranged apart from each other in the same space; positioning a substrate in the second heating furnace so that the substrate is adjacent to the second precursor and the second precursor is a mixture of tungsten trioxide (WO3) as a transition metal oxide and sodium chloride (NaCl) as a metal halide salt; forming a photosensitive layer containing transition metal dichalcogenide flakes on the upper part of the substrate; evaporating source and drain electrodes to form junctions on the photosensitive layer; and forming a gate electrode on the lower part of the substrate, wherein the mixing ratio of the transition metal oxide and the metal halide salt is 5:1 to 7:1 by weight.

Description

Technical Field

[0001] The present invention relates to an optical gate element, and more particularly, to an optical gate element including a transition metal chalcogenide as a photosensitive layer and a method for manufacturing the same.

Background Art

[0002] Autonomous driving has been studied since the 1970s. Entering the 2010s, combined with the emergence of deep learning technology, the technology has developed rapidly. Along with the period of the COVID-19 pandemic, the technology related to autonomous driving is developing even faster. In order to meet "artificial intelligence" and "safety", which are the core technologies of the future smart mobility industry, in order to recognize the lanes and obstacles in front of the vehicle, etc., the sensing element technology and the ultra-high-speed information processing such as recognition / judgment / control / operation are required. The importance of an artificial neuron network processing device equipped with neuromorphic technology that simultaneously performs information processing of recognition-perception-operation in parallel like the neuron structure and operation of the human brain is being maximized.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The present invention has been devised to solve the above-described problems, and an object thereof is to provide an optical gate element including a photosensitive layer capable of reacting to light stimulation and exhibiting neuromorphic characteristics and a method for manufacturing the same.

Means for Solving the Problems

[0004] To achieve the above technical problem, a method for manufacturing an optical gate device according to a preferred embodiment of the present invention includes the steps of: preparing a first heating furnace and a second heating furnace that are arranged separately from each other in the same space; positioning a first precursor containing a chalcogen substance in the first heating furnace, and positioning a substrate adjacent to a second precursor in which a transition metal oxide and a metal halide salt are mixed in the second heating furnace; heating each of the first heating furnace and the second heating furnace to different temperatures and performing molten salt-assisted thermochemical vapor deposition to form a photosensitive layer containing at least one or more transition metal dichalcogenide flakes on the substrate; and depositing an electrode to form at least two or more bonding sites on the photosensitive layer.

[0005] The mixing ratio of the transition metal oxide and the metal halide salt may be a weight ratio of 4:1 to 8:1.

[0006] The metal halide salt is represented by the general formula AZ or AZ2, where A is an alkali metal or an alkaline earth metal, and Z may be a halogen element.

[0007] The metal halide salt may include at least one selected from NaCl, NaBr, KCl, KBr, LiCl, LiBr, CaCl2, MgCl2, CaB2, MgBr2, and combinations thereof.

[0008] In the step of forming the photosensitive layer, the temperature of the first heating furnace may be 500°C or more and less than 700°C, and the temperature of the second heating furnace may be 700°C or more and less than 900°C.

[0009] The transition metal dichalcogenide flakes may be single-layer or multi-layered with two or more layers.

[0010] The average lateral length of the transition metal dichalcogenide flakes contained in the photosensitive layer may be 10 to 100 μm.

[0011] The electrode contains a metal or a metal compound, and the metal or the metal compound may contain a metal element selected from at least one of Ti, Ni, Au, Ag, and combinations thereof.

[0012] To achieve the above technical problem, a photogate device according to a preferred embodiment of the present invention includes a photosensitive layer disposed on a substrate and containing at least one or more transition metal dichalcogenide flakes, and a plurality of electrodes disposed in the photosensitive layer and spaced apart from each other.

[0013] The device may be a logic device that derives current characteristics associated with at least one of a photoelectric power applied in a pulsed manner from the outside and a voltage applied to a gate electrode, and performs logical operations of AND, OR, and summation operations by applying the photoelectric power with the derived current characteristics.

[0014] The device may be an artificial synapse device having a synapse characteristic that electrically simulates a synaptic reaction of a neuron with current characteristics derived by deriving current characteristics associated with at least one of a photoelectric power applied in a pulsed manner from the outside and a voltage applied to a gate electrode.

[0015] The synaptic reaction of the neuron may include learning (Potentiation) and forgetting (Depression) reactions due to a light stimulus applied in a pulsed manner.

[0016] The transition metal dichalcogenide flakes may be single-layer or multi-layer (two or more layers).

[0017] The average lateral length of the transition metal dichalcogenide flakes contained in the photosensitive layer may be 10 to 100 μm.

[0018] The electrode contains a metal or a metal compound, and the metal or the metal compound may contain a metal element selected from at least one of Ti, Ni, Au, Ag, and combinations thereof.

Advantages of the Invention

[0019] According to the present invention as described above, transition metal dichalcogenide flakes produced by the molten salt-assisted chemical vapor deposition method according to a preferred embodiment of the present invention can be grown uniformly and uniformly on a large-area substrate in a size range of several to several hundred micrometers. A photogate device using this as a photosensitive layer can perform logical operations of AND, OR, and summation operations by a reaction due to light stimulation, and has an effect that it can perform a synaptic operation reaction with low power.

[0020] The effects of the present invention are not limited to the effects described above, and are clearly understandable to those skilled in the art from the description throughout the specification. However, other effects not explicitly mentioned are also included as well.

Brief Description of the Drawings

[0021]

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Mode for Carrying Out the Invention

[0022] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The advantages and features of the present invention, and the method for achieving them, will become more apparent by referring to the embodiments described in detail below in conjunction with the accompanying drawings. However, the technical idea of the present invention is not limited to the embodiments disclosed below, and can be embodied in various different forms. Merely, the following embodiments complete the technical idea of the present invention and are provided to fully inform those with ordinary knowledge in the technical field to which the present invention pertains of the scope of the present invention. The technical idea of the present invention is only defined by the scope of the claims. Throughout the specification, the same reference numerals indicate the same components.

[0023] Also, unless otherwise specified in this specification or clearly inconsistent with the context, all terms used in this specification, including technical and scientific terms, can be used with meanings commonly understood by those with ordinary knowledge in the technical field to which the present invention pertains. Terms that are generally used and defined in a dictionary are not construed in an ideal or overly formal sense unless clearly defined in this application. The terms used in this specification are merely for the purpose of explaining the embodiments and are not intended to limit the present invention. In this specification, singular expressions include plural expressions unless clearly having other meanings in the context.

[0024] The phrases "comprises," "has," "includes," and "containing" used in this specification are to be construed as open-ended terms (i.e., meaning "including but not limited to") unless otherwise specified, and merely indicate the presence of the component, and are not to be understood as excluding the presence or addition of one or more other components, steps, operations, and / or elements.

[0025] An optical gate element including a transition metal dichalcogenide as a photosensitive layer FIG. 1 is a schematic diagram showing a cross-section of a light-gated element according to an embodiment of the present invention.

[0026] Referring to FIG. 1, a light-gated element 100 (Light-Gated Transistors; LGT) may be provided on a substrate 110 and include a photosensitive layer 120 containing a two-dimensional semiconductor material, and a plurality of electrodes 130 provided on the photosensitive layer 120 and spaced apart from each other.

[0027] The substrate 110 can use semiconductor substrates such as silicon and SOI (Silicon-on-insulator) as semiconductor materials. Specifically, a silicon substrate 111 with a dielectric layer 112 having a thickness of several to several hundred nanometers formed on its surface can be used. Also, wide-bandgap semiconductor substrates such as silicon carbide (SiC), gallium nitride (GaN), and gallium oxide (Ga2O3) can be used. The substrate 110 can further use a substrate doped with a dopant.

[0028] The photosensitive layer 120 is a layer that reacts by generating an electrical change when an applied optical signal is applied, and may contain a two-dimensional semiconductor material. The photosensitive layer 120 can be easily used as the photosensitive layer of a photogate element that can react to optical signals including near-infrared, visible light to ultraviolet wavelengths.

[0029] Specifically, the two-dimensional (2D) semiconductor material may have a structure in which strong covalent bonds are formed within a single layer and are bonded by relatively small van der Waals forces between layers. Different from ordinary photoelectric conversion elements, the two-dimensional semiconductor material can be immediately used as the photosensitive layer of a photoelectric conversion element with only a single material by using this direct transition property, which has the advantage of simplifying the structure of the element.

[0030] The two-dimensional semiconductor material may be arranged in a plate-like sheet having a layered structure within the photosensitive layer 120, for example, in a flake shape, and may be layered in a monolayer or a multilayer of two or more layers. Although the two-dimensional semiconductor material exhibits indirect transition characteristics in a bulk or normal-thickness thin film state, it exhibits direct transition characteristics when it is within a thickness of a single layer or several layers, has excellent photoreactivity, is transparent, and has flexible characteristics, so it can be effectively applied as an optoelectronic element.

[0031] In addition, the two-dimensional semiconductor material has a layered structure in which each layer retains a very strong covalent bond between constituent atoms and is bonded by weak Van der Waals forces between the layers. Since there are no dangling bonds extending outside the layer and there is only a two-dimensional interaction with the constituent atoms in principle, carrier transport shows an elastic transport mode, different from that of ordinary thin films and bulk materials. As a result, it can be applied as a semiconductor with high mobility, high speed, and low power.

[0032] Furthermore, since the two-dimensional semiconductor material has the advantage of being able to perform optoelectronic reactions sensitive to extremely small amounts of optical stimuli due to its atom-scale thin layered structure, it is possible to realize a learning ability in which the conductivity increases by reacting sensitively to the application of pulsed optical stimuli and a forgetting characteristic due to electrical stimuli.

[0033] The two-dimensional semiconductor material may include a transition metal dichalcogenide (TMD). Specifically, the transition metal dichalcogenide may be represented by the general formula MX2, where M is a transition metal element, for example, at least one selected from Mo, W, Nb, V, Ta, Ti, Zr, Hf, Tc, Re, Ru, Co, Pd, Pt, Cu, Ga, In, Sn, Ge, Pb, or combinations thereof, and X is a chalcogen element, which may include at least one selected from S, Se, Te, or combinations thereof. Specifically, the transition metal dichalcogenide material may include at least one selected from MoS2, MoSe2, MoTe2, WS2, WSe2, WTe2, ZrS2, ZrSe2, HfS2, HfSe2, NbSe2, ReSe2, PdTe2, or combinations thereof. More specifically, the transition metal dichalcogenide material may include at least one selected from MoS2, MoSe2, WS2, WSe2, or combinations thereof. In one aspect, it may include WSe2, but is not limited thereto.

[0034] The crystal structure of the two-dimensional semiconductor material has a covalent bond between M, which is a transition metal, and X, which is a chalcogen element. Based on this, it can have a hexagonal structure in the plane direction. It is also possible to mutate the crystal structure by performing further phase change steps or doping steps.

[0035] In particular, when the two-dimensional semiconductor material is provided as a transition metal dichalcogenide sheet, for example, a transition metal dichalcogenide flake, it is understood that the average lateral length is on the order of several to several hundred micrometers, for example, a transition metal dichalcogenide microflake. Specifically, the average lateral length of the transition metal dichalcogenide flake may be 10 - 100 μm, and in one aspect, it may be 50 - 60 μm, but is not limited thereto.

[0036] The electrode 130 may contain a metal or a metal compound. The metal or metal compound may contain a metal element including at least any one selected from Ti, Ni, Au, Ag, and combinations thereof, and any type of metal element suitable for application to electronic elements such as metal electrodes and metal interconnections can be used without limitation as long as it is of a type containing such a metal element.

[0037] Method for manufacturing transition metal dichalcogenide flakes FIG. 2 is a schematic diagram of a heating furnace used for the production of transition metal dichalcogenide flakes using a molten-salt-assisted chemical vapor deposition (SA-CVD) method according to an embodiment of the present invention.

[0038] Referring to FIG. 2, the production of transition metal dichalcogenide flakes using a molten-salt-assisted thermal chemical vapor deposition method used as a photosensitive layer of an optical gate element according to an embodiment of the present invention may first include a step of preparing a first heating furnace and a second heating furnace arranged apart from each other within the same space. The first heating furnace and the second heating furnace are connected by a quartz tube, and a carrier gas can flow through both ends.

[0039] Next, a first precursor containing a chalcogen substance may be positioned in the first heating furnace.

[0040] The first precursor is a chalcogen substance and may contain, for example, at least any one selected from S, Se, Te, or combinations thereof. In one aspect, the first precursor may be Se, but is not limited thereto.

[0041] Further, the second precursor may be positioned in the second heating furnace at a certain distance from the first precursor, and the substrate may be positioned adjacent to the second precursor.

[0042] The second precursor may be arranged at a certain distance while being located above the same space as the first precursor. The separation distance is a distance at which the precursor can be volatilized and transported in a vapor state in the heating furnace. Specifically, it may be 1 to 100 cm, more specifically, 10 to 70 cm, 20 to 60 cm, and in one aspect, it may be 20 to 40 cm, but it is not limited thereto.

[0043] The second precursor may be a mixed substance containing the transition metal oxide and the metal halide salt.

[0044] The transition metal oxide is a compound in which a transition metal (M) represented by the above-mentioned transition metal dichalcogenide substance (general formula MX2) is bonded to an oxygen atom. For example, it may be in the form of the general formula M x O y (where x and y are integers). Specifically, the transition metal oxide may mean an oxide of at least one selected from Mo, W, Nb, V, Ta, Ti, Zr, Hf, Tc, Re, Ru, Co, Pd, Pt, Cu, Ga, In, Sn, Ge, Pb or a combination thereof. For example, the transition metal oxide may be MoO, MoO2, MoO3, MoO x , Mo2O3, Mo2O5, WO, WO2, WO3, WO x , W2O3, W2O5, W 18 O 49 , W 20 O 58 , W 24 O 70 , W 25 O 73 , W 40 O 118It may contain NbO, NbO2, Nb2O3, Nb2O5, VO, VO2, V2O3, V2O5, Ta2O, Ta2O5, TiO2, ZrO, ZrO2, Zr2O3, Zr2O5, HfO2, Hf2O3, Hf2O5, etc. In one aspect, the transition metal oxide may be WO3, but is not limited thereto.

[0045] The metal halide salt serves as a catalyst to promote the synthesis of the precursor, and can control the shape and quality of the growth substance, specifically, the nuclear density, crystal size, shape, homogeneity, etc., by adjusting the ratio of the precursor mixed with the metal halide salt. Specifically, when applied to the chemical vapor deposition method, the metal halide salt can improve the reaction kinetics of the substance to be synthesized by increasing the vapor pressure. More specifically, the metal halide salt can react with the transition metal oxide to form a highly volatile molten salt having a high vapor pressure while having a low melting point. A chemical vapor deposition method assisted by such a molten salt may be performed. Therefore, by using the molten salt-assisted chemical vapor deposition method by the method including the metal halide salt, high-quality transition metal dichalcogenide flakes can be grown at a lower pressure and temperature than the normal chemical vapor deposition method including only the transition metal oxide as the precursor.

[0046] The metal halide salt may be represented by the general formula AZ or AZ2. At this time, A is an alkali metal or an alkaline earth metal, and Z may be a halogen element. For example, the metal halide salt may contain at least one selected from NaCl, NaBr, KCl, KBr, LiCl, LiBr, CaCl2, MgCl2, CaBr2, MgBr2, and combinations thereof. In one aspect, the metal halide salt may be NaCl, but is not limited thereto.

[0047] The thermochemical vapor deposition method using a molten salt, which is generated by mixing the transition metal oxide and the metal halide salt and will be described later, can lower the growth temperature of the transition metal dichalcogenide by promoting the reduction of the transition metal oxide. The mixing ratio of the transition metal oxide and the metal halide salt may be a weight ratio of 4:1 to 8:1, specifically, a weight ratio of 5:1 to 7:1. When having a mixing ratio within the above range, the average lateral length of the transition metal dichalcogenide flakes formed by the preferred manufacturing method of the present invention is large at the level of several to several tens of micrometers. For example, it can grow to about 50 to 60 μm. This may mean that it grows more uniformly to a larger size than the growth method without mixing the metal halide salt. However, if the mixing ratio of the metal halide salt increases compared to the transition metal oxide so as to deviate from the above range, the size of the formed transition metal dichalcogenide flakes can be reduced. In one aspect, the mixing ratio of the transition metal oxide and the metal halide salt may be a weight ratio of 6:1, but it is not limited thereto.

[0048] Next, a step of forming a photosensitive layer containing transition metal dichalcogenide flakes on the substrate by thermochemical vapor deposition of the first heating furnace and the second heating furnace at different temperatures from each other may be performed.

[0049] In the thermochemical vapor deposition process, a molten salt may be formed as an intermediate substance by the reaction of the metal halide salt and the transition metal oxide. The molten salt can lower the growth temperature of the transition metal dichalcogenide by promoting the reduction of the transition metal oxide. The molten salt formed at this time has the general formula A a M b O cIt may have a shape of (where a, b, and c are integers at this time). The molten salt is an intermediate substance that can be completely reacted and removed, and may be a substance that does not remain after the growth of transition metal dichalcogenide flakes as the final substance. When the assistance of the molten salt is not carried out, the synthesis of transition metal dichalcogenide may not proceed smoothly. The mechanism by which the above-mentioned transition metal dichalcogenide flakes are formed using the thermochemical vapor deposition method assisted by the molten salt can be explained, for example, according to the following Reaction Formula 1 to Reaction Formula 3. <Reaction Formula 1> 2WO 3(s) +2NaCl (s) →WO2Cl 2(g) +Na2WO 4(l) ……1 <Reaction Formula 2> Na2WO 4(l) +2H2Se (g) +H 2(g) →WSe 2(s) +3H2O (g) +Na2O (s) ……2 <Reaction Formula 3> WO2Cl 2(ads) +2H2Se (ads) +H 2(g) →WSe 2(s) +2H2O (g) +2HCl (g) ……3

[0050] First, NaCl, which is a metal halide salt, reacts with WO3, which is a transition metal oxide, to form gaseous WO2Cl2. At the same time, Na2WO4 can be formed as a molten salt with a low melting point and a high vapor pressure. The molten salt Na2WO4 is a substance with strong volatility and can react with H2Se, which is a chalcogen vapor saturated in the gaseous state in the heating furnace, to form WSe2 as a transition metal dichalcogenide. Also, WSe2 can be formed by the reaction of WO2Cl2 and H2Se. By including the metal halide salt, high-quality transition metal dichalcogenide flakes can be grown at a higher speed at a lower pressure and temperature than the chemical vapor deposition method containing only transition metal oxides as a precursor.

[0051] In addition, the growth temperature in the thermochemical vapor deposition process governs the deposition process, crystal nucleation, and the growth rate of the substance, and may directly affect the kinetics of the synthesized substance, which is a factor that can change the coverage of the thin film layer. The heating temperature of the first heating furnace where the first precursor containing a chalcogen substance is located may be 500°C or higher and less than 700°C, and in one aspect, it may be 600°C, but it is not limited thereto. Also, the temperature of the second heating furnace where the second precursor mixed with a transition metal oxide and a metal halide salt is located may be 700°C or higher and less than 900°C, and in one aspect, it may be 800°C, but it is not limited thereto.

[0052] The transition metal dichalcogenide flakes formed by heating the first heating furnace and the second heating furnace to perform thermochemical vapor deposition can be deposited on the substrate, and the deposition time is a factor that can change the coverage of the thin film layer. As the deposition time increases, the coverage range (coverage) covering the substrate can increase. The deposition time may be 1 to 10 minutes, specifically, it may be 3 to 9 minutes, and more specifically, it may be 5 to 8 minutes. When the thermochemical vapor deposition process is performed during the deposition time within the above range, it can have a coverage of 80% or more with respect to the area of the substrate. In one aspect, the deposition time of the thermochemical vapor deposition process may be 7 minutes, and the area of the transition metal dichalcogenide flakes produced thereby can have a coverage of 90% or more with respect to the area of the substrate.

[0053] In particular, by using the molten salt-assisted thermochemical vapor deposition method of the present invention, it is possible to lower the growth temperature by promoting the reduction of transition metal oxides with molten salts. In addition, since transition metal dichalcogenide flakes can simultaneously realize electrostatic gating using a dielectric and optical gating by applying an optical signal, there is an advantage that AND and OR logic operations can be realized in a single element by combining different gating methods.

[0054] Next, a step of depositing an electrode may be performed so as to form at least two or more bonding sites on the photosensitive layer.

[0055] The electrode may contain a metal or a metal compound. The metal or metal compound can contain at least one metal element selected from among Ti, Ni, Au, Ag, and combinations thereof, and any type of metal element that is suitable for application to electronic elements such as a metal electrode and a metal interconnection can be used without limitation as long as it is of a type containing such a metal element.

[0056] The step of depositing the electrode can use, without limitation, methods for depositing a metal thin film to which energy at a level that does not induce defects in the photosensitive layer is applied, such as an electron beam evaporator, a thermal evaporator, sputtering, and the like.

[0057] Hereinafter, the present invention will be described in more detail using examples and comparative examples. However, the following examples and comparative examples are for illustrative purposes of the present invention, and the scope of the present invention is not limited thereto.

[0058] Production Example 1: Growth of WSe layer using molten salt-assisted chemical vapor deposition (SA-CVD) method 2 Growth of layer A quartz boat containing 48 mg of selenium (Se, >99.5%) powder was placed in a primary heating furnace, and a quartz boat containing a mixed powder of 24 mg of tungsten trioxide (WO3, 99.9%) powder and 4 mg of sodium chloride (NaCl, >99.0%) was placed in a secondary heating furnace. On the other hand, a 2.5 cm x 2.5 cm silicon wafer with a 300 nm thick SiO2 insulating layer was placed in the secondary heating furnace containing WO3 / NaCl. The distance between the two quartz boats was optimized to 34 cm in a quartz tube, and the quartz tube was evacuated to 10 -2 Torr and then Ar was flowed in at 100 sccm as a carrier gas. After that, the primary heating furnace and the secondary heating furnace were heated at ramp rates of 10.9 °C / min and 14.5 °C / min, respectively. As a result, WSe2 was grown under the condition that the temperature of the primary heating furnace containing Se was 600 °C and the temperature of the secondary heating furnace containing WO3 / NaCl was 800 °C, and Ar was continuously flowed in at a flow rate of 100 sccm and H2 was flowed in at a flow rate of 20 sccm and held for 7 minutes during the WSe2 growth process. After the reaction was completed and the heating furnace was cooled, a wafer substrate with multiple layers of WSe2 flakes grown was obtained using the molten salt-assisted thermochemical vapor deposition method.

[0059] Production Example 2: Growth of WSe layer using chemical vapor deposition (CVD) method 2 Growth of layer Except that instead of using a mixed powder of tungsten trioxide (WO3) powder and sodium chloride (NaCl), only tungsten trioxide (WO3) powder was used excluding sodium chloride (NaCl), a wafer substrate with WSe2 flakes grown was obtained in the same manner as in Production Example 1.

[0060] Experimental Example 1: Confirmation of physical properties of transition metal dichalcogenide flakes grown by molten salt-assisted chemical vapor deposition method Figure 3 shows (a) an optical photograph, (b) an optical microscope image, (c) the coverage (%) as a function of the thermochemical vapor deposition time, and (d) the X-ray photoelectron spectroscopy (XPS) results of transition metal dichalcogenide flakes grown by the molten salt-assisted thermochemical vapor deposition method according to Production Example 1 of the present invention. Figure 4 shows (a) the atomic force microscopy (AFM) results, (c) the height profile, (b) the Kelvin probe force microscope (KPFM) image, and the contact potential difference (CPD) profile of the transition metal dichalcogenide flakes according to Example 1 of the present invention.

[0061] Referring to FIGS. 3 to 4, it can be confirmed that the transition metal dichalcogenide flakes synthesized by the molten salt-assisted thermochemical vapor deposition method grew uniformly on the SiO2 / Si substrate. When the heating temperature of the second heating furnace containing the second precursor in which the transition metal oxide and the metal halide salt were mixed was 800° C. and the deposition time was 7 minutes, it was confirmed that a very high coverage of approximately 95% was exhibited. This result is an excellent result showing a high coverage while the produced transition metal dichalcogenide material retains the 2H phase. In addition, it can be confirmed that the produced transition metal dichalcogenide flakes have a smooth surface without roughness and a uniform thickness over the entire area of the flakes. By performing a profile scan, it can be confirmed that the single-layer transition metal dichalcogenide flakes have a thickness of approximately 0.7 nm. In addition, the transition metal dichalcogenide flakes composed of two layers, three layers, and multiple layers were formed to have thicknesses of 1.5 nm, 2.2 nm, and 6.5 nm, respectively. Furthermore, the work function difference between the single-layer transition metal dichalcogenide flakes and the Si / SiO2 substrate was approximately 0.1 V.

[0062] Figure 5 shows (a) Raman analysis of single-layer (1L), bilayer (2L), trilayer (3L), and multi-layer (Multi-L) transition metal dichalcogenide flakes synthesized by the molten salt-assisted thermochemical vapor deposition method according to Production Example 1 of the present invention, and (b) E 1 2g vibration mode (251 cm -1 for the transition metal dichalcogenide flakes, (c) photoluminescence (PL) results for the transition metal dichalcogenide flakes according to the number of layers, and (d) photoluminescence intensity mapping (PL intensity mapping) results for the single-layer transition metal dichalcogenide flakes on the SiO2 substrate.

[0063] Referring to FIGS. 5a and 5b, the transition metal dichalcogenide (WSe2) flakes synthesized by the molten salt-assisted thermochemical vapor deposition method were confirmed to have a 2H-phase crystal structure by Raman analysis. The Raman spectrum has in-plane vibration modes (E 1 2g ) and out-of-plane vibration modes (A 1g ) corresponding to peaks at approximately 250 cm -1 and 260 cm -1 . On the other hand, a peak was observed at approximately 304 cm 2g 1 in the interlayer interaction mode (B -1 ). From this, it can be seen that although no peak was observed at approximately 304 cm -1 in the single-layer (denoted as 1L) sample, this peak was confirmed for the multi-layer (denoted as 2L, 3L, and Multi-L) samples. Using the Raman intensity mapping results, the E 1 2g vibration mode (251 cm -1) In the Raman intensity mapping for monolayer WSe2 flakes, it can be confirmed that the Raman intensity is uniformly distributed over the entire area of the transition metal dichalcogenide flakes.

[0064] Referring to FIGS. 5c and 5d, using the photoluminescence (PL) results, it can be confirmed that for the transition metal dichalcogenide monolayer peak, a high intensity is shown, while for the multi-layer (bilayer and multi-layer) peaks, as the number of layers increases, the peak intensity decreases. As a result of performing PL mapping on 0.7 nm monolayer transition metal dichalcogenide (WSe2) on a SiO2 substrate, it can be confirmed that a uniform intensity is shown.

[0065] FIG. 6 shows (a) high-resolution transmission electron microscope (HRTEM) for the SiO2 / WSe2 / Pt cross-sectional layer of the transition metal dichalcogenide flakes synthesized by the molten salt-assisted thermochemical vapor deposition method according to Production Example 1 of the present invention, and (b) the results of energy dispersive X-ray spectroscopy (EDS) thereof.

[0066] Referring to FIG. 6, it can be confirmed that the thickness of the WSe2 grown on the SiO2 substrate formed by the molten salt-assisted thermochemical vapor deposition method of the present invention is about 3 nm, and it can be confirmed that the thin film forms a uniform and flat thin film from a two-dimensional material and no impurities are detected in the TEM-EDS elemental mapping analysis.

[0067] Figure 7 shows an optical photograph of transition metal dichalcogenide flakes synthesized using a molten salt-assisted thermochemical vapor deposition method according to Production Example 1 of the present invention on a 2x2 inch substrate and 25 locations used for photoluminescence (PL) measurement. Figure 8 shows (a) in-plane vibration mode (E 1 2g ) and out-of-plane vibration mode (A 1g ) corresponding to Raman results at approximately 250 cm -1 and 260 cm -1 and photoluminescence (PL) results of a SiO2 substrate (1.62 eV) collected at 25 locations within the substrate on which transition metal dichalcogenide flakes synthesized by the molten salt-assisted thermochemical vapor deposition method according to Production Example 1 were grown.

[0068] Referring to Figures 7 and 8, it can be confirmed that all 25 locations within the substrate on which transition metal dichalcogenide flakes synthesized by the molten salt-assisted thermochemical vapor deposition method were grown show uniform Raman and photoluminescence analysis results consistent with WSe2, and it can be confirmed that transition metal dichalcogenide flakes with uniform quality characteristics can be grown over the entire area of the substrate even when using a large-area 2x2 inch substrate.

[0069] Example 1: An optical gate element including WSe flakes produced by using molten salt-assisted chemical vapor deposition (SA-CVD) method as a photosensitive layer 2 Growth of layer A wafer substrate on which a WSe2 layer produced by the method of Production Example 1 was grown was used as a photosensitive layer, and then 50 nm of nickel (Ni) was deposited using an electron beam evaporator to form a metal electrode on the substrate. Thereby, a plurality of electrode layers separated from each other and laminated on WSe2, that is, a WSe2 / Ni interface was produced, and a photogate element including WSe2 flakes produced using a molten salt-assisted chemical vapor deposition (SA-CVD) method as a photosensitive layer was manufactured.

[0070] Experimental Example 2: Measurement of electrical characteristics of the element The electrical properties of an optical gate device including a transition metal dichalcogenide flake synthesized by the molten salt-assisted thermochemical vapor deposition method of the present invention as a photosensitive layer were measured using a probe system (4200A-SCs, manufactured by Keysight Technologies) semiconductor parameter analyzer in a darkroom under ambient conditions. Raman spectra were obtained at room temperature under ambient pressure using a Raman spectrometer (DXR2xi, manufactured by Thermo Fisher Scientific) with a 532 nm laser and an incident laser power of 6.1 mW, and spectra in the range of 50 to 3500 cm -1 were obtained. The topography of a 30 μm x 30 μm region of the optical gate device and the Kelvin probe image was collected using an atomic force microscope (MFD-3D Origin (trademark) AFM, manufactured by Oxford Instruments) in non-contact and scanning probe microscope (SKPM: Scanning Kelvin Probe Microscopy) mode. Fourier transform infrared spectroscopy (FT-IR) spectra were obtained at room temperature using an FR-IR spectrophotometer spectrometer (Nicolet (trademark) iS50, manufactured by Thermo Fisher Scientific). Analysis by X-ray photoelectron spectroscopy (XPS) was performed using a Thermo Scientific (trademark) Nexsa (trademark) G2 surface analysis system as an X-ray photoelectron spectroscopy (XPS) system. As the spectrometer used for photoluminescence, it was obtained at room temperature using a PL (manufactured by Nanobase) device, and the cross-sectional height profile was measured using a Themis-Z (trademark) TEM (transmission electron microscope) device manufactured by FEI.

[0071] Figure 9 shows (a) a schematic diagram and a circuit diagrammatic view, and (b) a constant V when an optical gate device including a transition metal dichalcogenide flake synthesized by the molten salt-assisted thermochemical vapor deposition method according to Example 1 of the present invention is used as a normal back-gated transition metal dichalcogenide field effect transistor (back-gated FET). DS (1V) at V BG(a) P-type transmission characteristics measured by swiping from -50V to +50V and (c) output I-V results obtained by swiping from -10V to +10V at different gate biases.

[0072] Figure 10 shows (a) a schematic diagram and a circuit diagrammatic view, (b) transmission characteristics under different optical gate powers, and (c) V from -10V to +10V under the threshold optical power, with an optical power of 405 nm applied to a photogate device including a transition metal dichalcogenide flake synthesized by the molten salt-assisted thermochemical vapor deposition method according to Example 1 of the present invention as a photosensitive layer. DS Output I-V results under various optical gate powers in the range of 0.2 to 1.0 mW under swipe.

[0073] Referring to FIGS. 9 and 10, it can be confirmed that the photogate device including a transition metal dichalcogenide flake synthesized by the molten salt-assisted thermochemical vapor deposition method according to Example 1 of the present invention can be driven in both FET and LGT modes during electrical gating and optical gating. Referring to FIG. 9, in a back-gate transistor device based on WSe2 using a back-gate swipe V from -50V to +50V at a constant V DS = 1V, p-type transmission characteristics were measured. The FET device has a gate voltage at the upper end of 92.35 cm BG V 2 V -1 s -1It exhibits hole mobility with p-type dominant driving characteristics having bipolar behavior. Referring to FIG. 10, the same device can be optically gated by photoelectric power in the same manner. When the optical gate is illuminated, the photo-generated charge carriers can modulate the conductivity of the light-sensitive region, which will gradually modulate the electrical behavior of the transistor. The output characteristics of the optical gate transistor can be adjusted by the output current or voltage and the input light intensity, wavelength or other related parameters. The optically gated transistor exhibits high sensitivity and fast response time, and the photoelectric power of other outputs can provide multiple "ON" states. Therefore, the device of the present invention can be used as an integrated device that can be driven by a device capable of both electrical signal processing and light sensing.

[0074] FIG. 11 shows (a) the dynamic driving mode under pulse modulation of light irradiation under threshold optoelectronic power, (b) the logic operation based on a single device with simultaneous input of electrical gating and optical gating, and (c) the synaptic function mode inspired by the brain for the threshold optical power of the optical gate device including a transition metal dichalcogenide flake synthesized by the molten salt-assisted thermochemical vapor deposition method according to Example 1 of the present invention as a photosensitive layer.

[0075] Referring to FIG. 11, a light-gated transistor (LGT) including a transition metal dichalcogenide flake synthesized by the molten salt-assisted thermochemical vapor deposition method according to Example 1 of the present invention as a photosensitive layer can exhibit the ability to induce photoreaction and generation of postsynaptic current. The synaptic weight value in the LGT is complexly connected to various parameters including the power, duration, and frequency of the applied stimulus. In relation to power, it is important to exceed a specific threshold energy barrier for any transmission between different states to occur, and this phenomenon is substantially the same as the phenomenon in biological neurons where the signal intensity must exceed a specific threshold to enable the formation of synapses between continuous axons. Similarly, in a solid-state synaptic device, regardless of whether the stimulus is essentially electrical, optical, or chemical, it must exhibit an intensity exceeding the threshold for effective operation and state transition. When there is no optical stimulus, the device remains non-responsive and does not induce an observable output. However, when a relatively low-intensity optical stimulus below the threshold is applied, it triggers a carrier-based optical response, and although such a response is detectable, it is not sufficient to set a significant synaptic weight value. In contrast, when the intensity of the stimulus exceeds the threshold barrier (P TH shown at), a conversion occurs. The normal optical response evolves into a synaptic response characterized by a non-zero synaptic weight value. Such a transition means the ability of the device to store and process information substantially similar to short-term memory. In particular, when the laser power level varies within the range of 0.2 - 0.8 mW (refer to FIG. 10 again), the LGT shows a synaptic weight value of 0 and exhibits behavior consistent with sensory perception. However, when the laser stimulus intensity exceeds 1 mW, it completes with a non-zero synaptic weight value and undergoes a transition to a state substantially similar to short-term memory in sensory behavior. Such a change in function indicates that the LGT is excellent in information processing and memory, and is applicable to both a photodetector and an electronic synaptic device, especially from the perspective of the pulse strategy of a sensory memory system.

[0076] FIG. 12 shows the results of (a) 405 nm wavelength and 0.2 to 0.8 mW / cm 2 of an optical gate device including, as a photosensitive layer, transition metal dichalcogenide flakes synthesized by the molten salt-assisted thermal chemical vapor deposition method according to Example 1 of the present invention. 2 (b) Dynamic photoresponse results generated at a laser source of power, (b) photoresponse results across the operating frequency spectrum ranging from 1.4 Hz to 0.1 Hz, and (c) response characteristics.

[0077] Referring to Figure 12, the light-induced dynamic driving characteristics of the WSe2 LGT were evaluated under both dark conditions and laser (405 nm) illumination. Figure 12a shows the temporal photoresponse across a range of optical source powers, from 0.2 mW to 0.8 mW, when the gate voltage was zero. The measured response remained consistent and reproducible for multiple consecutive ON / OFF cycles at each power level. Such stability and repeatability demonstrate the robust performance of the LGT dynamic response, further highlighting its high sensitivity. Furthermore, the LGT exhibits excellent photoresponse across the optical operating frequency spectrum, ranging from a high of 1.4 Hz to a low of 0.1 Hz. The remarkable photodetection performance observed at various power levels and frequencies indicates its suitability for various optical communication devices. The rise time for each optical signal frequency was approximately 60 ms, while the decay time was approximately 50 ms, demonstrating fast response characteristics. This demonstrates the excellent performance of the LGT-based photodetector, characterized by high sensitivity, cycling stability, and applicability across the optical operating frequency range. These attributes make them applicable to a variety of optical communication and sensing devices.

[0078] FIG. 13 shows (a) the response of an optical gate device containing transition metal dichalcogenide flakes synthesized by the molten salt-assisted thermal chemical vapor deposition method according to Example 1 of the present invention as a photosensitive layer, and (b) the specific detectability analysis for each bias across the channel.

[0079] Referring to Figure 13, responsivity (R) is an important parameter that quantifies the sensitivity of a detector to incident optical power. The optical power (P O ) versus the amount of photocurrent (I ph ) is precisely calculated as a ratio of the photodetector's responsivity (R) and non-detectability (D). This parameter is a fundamental measure that provides valuable insight into the performance characteristics of a photodetector that converts incident photons into electrical current. * Detectivity) is a parameter for evaluating the photodetector performance of an LGT device, and can be expressed by the following Equations 1 and 2:

[0080]

number

[0081]

number

[0082] where λ is the wavelength, q is the charge of the electron, h is Planck's constant, c is the speed of light in a vacuum, and D * is the degree of non-detection, and J dark is the dark current density.

[0083] In terms of responsivity and detectability, the optical gate element of the present invention is highest when an optical power source of 0.2 mW is used, with the respective values being responsivity of approximately 40 μA / W and detectability of approximately 3.16×10 9 cmHz 0.5 W -1However, this performance metric appears to decrease as the optical power increases above this threshold value. This decrease in responsivity and non-detectability indicates the presence of specific trap states within the optical gate element. Such deviations from ideal operation indicate the presence of non-ideal characteristics of the optical gate element, such as trap states and limited charge carrier extraction.

[0084] FIG. 14 is an analysis of a transistor logic using an optical gate device containing, as a photosensitive layer, transition metal dichalcogenide flakes synthesized by the molten salt assisted thermal chemical vapor deposition method according to Example 1 of the present invention.

[0085] Referring to FIG. 14a, a series of inputs can be demonstrated using a 5mW optical gate as IN-1 and a +5V electrical gate as IN-2, resulting in an AND logic output. Referring to FIG. 14b, a series output can be demonstrated using a 5mW optical gate as IN-1 and a -5V electrical gate as IN-2, resulting in an OR logic output. Referring to FIGS. 14c and 14d, the LGT and amplifier response can be output as a summation operation, where the single A and B responses are summed to generate A+B. Here, a 5mW laser optical gate was used as IN-A and a 1mW LED gate was used as IN-B. The input data is displayed in black / blue, and the output logic function of the device is displayed in red.

[0086] FIG. 15 shows (a) excitatory postsynaptic behavior as a function of the number of pulses under a positive bias of the back gate electric field, (b) inhibitory postsynaptic behavior as a function of the number of pulses under a negative bias of the back gate electric field, and (c) optimized excitatory postsynaptic current (EPSC) and inhibitory postsynaptic current (IPSC) characteristics when the gated bias field for efficient power consumption is not small, for an optical gate device including a photosensitive layer of transition metal dichalcogenide flakes synthesized by the molten salt-assisted thermal chemical vapor deposition method according to Example 1 of the present invention.

[0087] 15a to 15c, the synaptic characteristics of the optical gate device can be confirmed by applying a 405 nm wavelength laser stimulus with a power of 1 mW operating at a source frequency of 1 Hz when the laser gating power exceeds the threshold voltage. DS ) was held at a constant value of 1.0 V, whereas the back gate voltage (V BG ) was varied across 10, 20, and 30 V for excitatory postsynaptic currents (EPSCs). For inhibitory postsynaptic currents (IPSCs), V BGIt was adjusted to -10V, -20V, and -30V. Based on the p-type semiconductor characteristics of the photosensitive layer, as the back-gate potential increases, the transmission intensity of the gating weight value decreases. The optical gate device including the transition metal dichalcogenide flake according to the present invention as the photosensitive layer can be confirmed to show a gradual progression of EPSC and IPSC operations according to the learning (FIG. 15a) and forgetting (FIG. 15b) dynamics based on the pulse stimuli affected by both the polarity and magnitude of the back-gate field. In particular, considering that as the back-gate field becomes larger, the gating responses to both EPSC and IPSC are saturated earlier, the optical gate device including the transition metal dichalcogenide flake according to the present invention as the photosensitive layer shows the ability to exhibit a learning operation even in the absence of a back-gate field. As shown in FIG. 15c, it can be adjusted to display a very small negative-polarity forgetting operation applied to V BG =-5V like V BG is applied. At V BG =0V, a conductance state in the optical range is observed and spreads until saturation is reached. This can indicate that the device can operate efficiently at a lower power level and is driven by a synaptic operation with reduced energy consumption.

[0088] FIG. 16 shows the (a) EPSC and IPSC characteristic results associated with the pulse duration and (b) the paired pulse facilitation (PPF: when the presynaptic cell is stimulated continuously, the second synaptic transmission is facilitated compared to the first synaptic transmission) and paired pulse depression (PPD: when the presynaptic cell is stimulated continuously, the second synaptic transmission is depressed compared to the first synaptic transmission) characteristic results of the optical gate device including the transition metal dichalcogenide flake synthesized by the molten salt-assisted thermochemical vapor deposition method according to Example 1 of the present invention as the photosensitive layer.

[0089] Referring to FIGS. 16 and 17, the excitatory postsynaptic current (EPSC) and inhibitory postsynaptic current (IPSC) induced by pulsed laser stimulation were measured at a constant back-gate voltage (V BG ) of 10 V and -10 V, respectively. It can be confirmed that as the duration of the laser pulse increases from 50 ms to 550 ms, the EPSC and IPSC responses show a tendency of gradual saturation. Such behavior is substantially similar to the mechanisms of paired pulse facilitation (PPF) and paired pulse depression (PPD) of observable paired stimuli in biological neurons, which play important roles in information processing within neural networks. In particular, it can be confirmed that the EPSC induced by the response to the second laser pulse is even larger than the response to the first pulse. Conversely, it can be confirmed that the response of the IPSC to the second laser pulse is reduced compared to the first laser pulse. Such results are consistent with the characteristics known as synaptic responses in biological systems and should be understood as results indicating synaptic characteristics and compatibility with this function.

[0090] As described above, the embodiments of the present invention have been described based on the accompanying drawings. Those having ordinary knowledge in the technical field to which the present invention pertains should be able to understand that other specific forms of the present invention can also be implemented without changing the technical idea and essential features of the present invention. Therefore, the above-described embodiments should be understood as being exemplary in all aspects and not limiting.

Explanation of Reference Numerals

[0091] 100 Optical gate element 110 Substrate 111 Silicon 112 Insulating layer 120 Photosensitive layer 130 Electrode

Claims

1. In a method for manufacturing a photogate device, a step of preparing a first heating furnace and a second heating furnace that are arranged separately from each other within the same space; Position a first precursor containing a chalcogen substance in the first heating furnace, and tungsten trioxide (WO ３ ) and sodium chloride (NaCl) as a metal halide salt are mixed, and position a substrate adjacent to the second precursor. heating each of the first heating furnace and the second heating furnace to different temperatures and performing molten salt-assisted thermochemical vapor deposition to form a photosensitive layer containing at least one or more transition metal dichalcogenide flakes having an average lateral length of 50 to 60 μm on top of the substrate; a step of depositing a source electrode and a drain electrode so as to form at least two or more bonding sites on the photosensitive layer; a step of forming a gate electrode under the substrate; comprising, the mixing ratio of the transition metal oxide and the metal halide salt is a weight ratio of 6:1; the device is a logic device that derives current characteristics by a combination of photoelectric power applied in a pulsed manner from the outside to the photosensitive layer and a positive voltage or a negative voltage applied to the gate electrode, and performs AND or OR logical operations. A method for manufacturing a photogate device.

2. In the step of forming the photosensitive layer, the temperature of the first heating furnace is 500 °C or higher and less than 700 °C, the temperature of the second heating furnace is 700 °C or higher and less than 900 °C. The method for manufacturing a photogate device according to Claim 1.

3. The transition metal dichalcogenide flakes are single-layer or two-layer or more layered. The method for manufacturing a photogate device according to Claim 1.

4. The source electrode and the drain electrode contain a metal or a metal compound, the metal or the metal compound contains at least one metal element selected from among Ti, Ni, Au, Ag, and combinations thereof. The method for manufacturing a photogate device according to Claim 1.

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